1. Field of the Invention
The present invention relates to a vehicle power transmission and more particularly to a belt-pulley type steplessly variable power transmission. More specifically, the present invention pertains to a belt-pulley type steplessly variable transmission capable of a reverse drive as well as a forward drive.
2. Description of Prior Art
It has hithertofore been proposed to use a belt-pulley type transmission for automobile driving systems. In such driving systems, the transmission is required to have an ability of transmitting the engine rotation in a reverse direction as well as in a forward direction. For the purpose, the transmission is provided with a reverse drive gear mechanism. For example, Japense patent application 49-105564 filed Sept. 13, 1974 and disclosed for public inspection on Mar. 22, 1976 under the disclosure number 51-33422 discloses a belt-pulley type transmission having a forward-reverse selecting gear mechanism provided between the power clutch and the input member of the belt-pulley mechanism. In the proposed transmission, however, problems have been encountered in that the direction of rotation of the input member of the belt-pulley mechanism is changed between the forward and reverse drive modes. Such change in the direction of rotation of the input member causes a change in the direction of the torque which is being transmitted by the belt so that the life of the belt is shortened to an undesirable extent. Further, in the proposed transmission, the speed ratio is changed not only in the forward drive mode but also in the reverse drive mode. This property is undesirable because the vehicle speed may be increased not under the will of the operator but under the load on the transmission. The problem may be overcome by locking the transmission at a specific speed ratio, however, a complicated locking mechanism is required for the purpose.